1. Field of the Invention
The present invention relates to a laser light source for outputting laser light with a high power and a short pulse by using the Q-switching technology.
2. Related Background Art
Laser light sources have been under study and development for attaining higher power, shorter pulse, and shorter wavelength in output light. In particular, attention has been directed toward laser light sources using the Q-switching technology. As a configuration having not only a laser medium but also a Q-switching device within a resonator, the Q-switching technology regulates the laser oscillation by changing the Q-value of resonator with the Q-switching device, thereby causing the laser light outputted therefrom to have a shorter pulse and a higher power.
Various techniques have been known as the Q-switching technology. Among them, the passive Q-switching technique using a saturable absorber as a Q-switching device is preferable in that its laser light source has a configuration simpler and smaller than that in other Q-switching techniques. The saturable absorber exhibits a smaller absorption as the incident light power is higher, and absorbs the incident light when the incident light power is not higher than the absorption saturation threshold, but saturates its absorption and becomes transparent when the incident light power exceeds the absorption saturation threshold. By utilizing such a property, the saturable absorber is used as a Q-switching device.
Namely, a laser light source using a saturable absorber as a Q-switching device operates as follows. At the time when the pumping of a laser medium is started, the laser medium has a small population inversion, whereby the light incident on the saturable absorber after being emitted from the laser medium has a low power. Therefore, at the time when the pumping of the laser medium is started, the saturable absorber exhibits a large absorption and is opaque, whereby the Q-value of resonator is so small that no laser oscillation occurs. Even in a period where the Q-value of resonator is so small that no laser oscillation occurs, the laser medium is continuously pumped, so that the population inversion of the laser medium gradually increases, whereby the light incident on the saturable absorber after being emitted from the laser medium gradually enhances its power. Then, when the power of light incident on the saturable absorber after being emitted from the laser medium exceeds the absorption saturation threshold, the saturable absorber drastically decreases its absorption (i.e., becomes transparent), whereby the resonator enhances its Q-value, so that stimulated emission drastically advances in the laser medium. As a result, a laser oscillation occurs. Thus, pulsed laser light having a high power and a short pulse is outputted from the resonator.
On the other hand, various laser media have been known, whereas various pumping means have been known as those pumping the laser media. For example, Nd:YAG crystal is used as a laser medium, whereas a semiconductor laser light source is used as pumping means for pumping the laser medium upon irradiation with pumping light. In this case, Nd:YAG crystal acting as a laser medium is irradiated with the pumping light outputted from the semiconductor laser light source, so that Nd ions contained in this laser medium are pumped to an upper level, which generates a population inversion. The operation of passive Q-switching is as mentioned above.
Semiconductor laser pumping solid-state laser light sources using such a passive Q-switching technique are favorable in that their configuration is simple and smaller in size. Such a laser light source can be made smaller as a whole since its resonator length may be shorter, and is suitable for outputting pulse laser light having a short pulse.